Micromegas prototypes with thermo-bond film separators

In this paper we report the results of Micromegas prototypes constructed by attaching micromesh to an anode using thermo-bond films. The excellent metal attaching ability and good dielectical property of this kind of film make it a promising material to be used as avalanche gap spacers. Several prototypes are successfully made. The electron transmission properties are first studied and then the gas gain is measured in argon-isobutane mixtures. The maximum gain of more than 10⁴ is easily obtained. The energy resolutions for ⁵⁵Fe 5.9 keV K_α ray can be better than 20% over one magnitude in gain for different operational gas mixtures and the best energy resolution of 13.7% (FWHM) can be achieved with the gas mixture of 94% argon concentration. The preliminary test results of the prototypes with sensitive area of 45 mm×45 mm without internal support show good uniformity across the sensitive area.     

B/Al/Ga-MOR分子筛催化甲醇/二甲醚羰基化反应机理的理论计算研究

采用DFT计算比较分析了B、Al和Ga分别同晶取代MOR分子筛八元环侧袋T3位点及十二元环孔道T4位点时甲醇及二甲醚羰基化反应机制的共性及差异。研究发现,CO插入甲氧基生成乙酰基的反应遵循S_N2机制,且为羰基化反应过程中的决速步;473 K下,无论甲醇或二甲醚为原料,生成的乙酰基更倾向于与甲醇中的CH₃O作用生成乙酸甲酯;T3位点具有更好的羰基化择形性,而T4位点上更倾向于发生由三甲基氧鎓离子生成芳烃导致催化剂失活的副反应。与Al-MOR相比,在T3位点引入B和Ga会导致羰基化反应能垒的升高,降低其催化性能;而在T4位点引入B和Ga(尤其是B)则可大幅提升其生成三甲基氧鎓离子的能垒,抑制芳烃生成过程,提升催化剂稳定性。本工作有助于认识MOR分子筛不同孔道内酸性位点发生同晶取代时催化羰基化反应机制的差异,为调控设计高效MOR沸石催化剂提供一定的理论支撑。     

A new gaseous detector — micro mesh gaseous structure

The structure and working principle of Micromegas （MICRO Mesh Gaseous Structure） is discussed. Some radiation sources of α and X rays are used to test this detector. The optimized electric-field intensity of the conversion gap is obtained. The transmission of electrons and the uniformity of the amplification gap are also presented. The energy resolution of the 5.9 keV peak is better than 27%.     

3MW_(th)富氧燃烧煤粉锅炉的数值模拟研究

以国内首台3 MW_(th)富氧燃烧煤粉锅炉为研究对象,借助CFD软件对煤粉空气燃烧和富氧燃烧工况进行数值模拟研究。通过与实验结果对比发现,模拟得到的炉膛温度分布、换热量以及出口组分与实验测量结果吻合,这表明本文使用改进的辐射特性模型以及4步化学反应机理能够很好地预测炉内温度、传热以及烟气组分分布。通过模拟研究,对比分析了空气燃烧与富氧燃烧的炉内特性。研究结果表明:富氧燃烧时,CO_2的显著增加使得燃烧器区域出现高浓度CO;富氧燃烧的整体温度分布与空气燃烧相似,但峰值温度有较大的降低;炉内辐射传热较空气燃烧略有下降。     

富氧燃烧条件下煤焦的燃尽特性

本文利用平面火焰携带流反应器研究了DT烟煤在富氧燃烧条件下的燃烧实验。采用灰示踪法分析煤焦的燃尽和元素释放特性,并采用等密度模型计算了基于氧化反应C+0.5O_2→CO的表观反应动力学参数。研究结果表明;煤粉在富氧燃烧条件下的燃尽慢于空气燃烧;富氧燃烧条件下,煤焦与CO_2的气化反应会导致煤焦表面对O的化学吸附,进而导致氧元素释放速率减慢;高氧浓度条件下,高浓度CO_2对煤焦燃尽的抑制作用大于CO_2气化反应对煤焦燃尽的促进作用,降低环境氧浓度可以逐步提高CO_2气化反应对煤焦燃尽的贡献。     

3D simulation of micromegas detector performance

Micromegas （MICRO MEsh GAseous Structure） is a position-sensitive gaseous detector. It is widely used in particle physics. We present the results of full 3D Monte Carlo simulations of Micromegas performance, taking into account all the processes from the primary ionization, the elctron collection efficiency, and the gain to the signal formation. The simulation results are in good agreement with experimental data.